1. Field of the Invention
The present invention relates to a MAC (Media Access Control) address notification method in MPOA (Multi-Protocol Over ATM (Asynchronous Transfer Mode)) systems.
2. Description of the Prior Art
The Conventional MPOA system is a communication system for existing network layer protocols such as Internet Protocol (hereinafter, called as IP), and Internetwork Packet Exchange (hereinafter, called as IPX) on asynchronous transfer mode (hereinafter, called as ATM) networks, and the specifications are defined by the ATM Forum's document AF-MPOA·0087.000. The feature of the MPOA system is that, when a destination node (target) is in a subnet different from that of a source node as viewed from the source node of data packets, communication is performed not through routers, but through a shortcut VC (Virtual Channel) toward the target in an ATM network, when a data flow (flow of continuous data packets) rate larger than a predetermined value is detected.
The operations of the conventional MPOA system will be described. Hereinafter, IP is used as a network layer protocol for the description, but the above protocol is not limited to IP.
The operations depend on whether the target is on the ATM network or not. In the first place, the operations for a case where the target is on the ATM network will be described, referring to FIG. 14.
It is assumed that a node of an MPC (MPOA Client) 701 starts to transmit IP packets toward a target 704. The IP packets are forwarded hop by hop through a node of a MPC 701, that of an MPS (MPOA Server) 702, and that of an MPS 703, toward the target 704.
During the above time, the MPC 701 counts the IP packets. When the above counted value becomes equal to or larger than a predetermined value in a fixed time, (for example, equal to or larger than ten packets in one second), it is judged as “There is a flow”.
The MPC 701 which detects the above flow transmits an MPOA Resolution Request packet which includes the IP address of the target 704 to the MPS 702.
The MPS 702 makes an NHRP (NBMA (Non-Broadcast Multi-Access) Next Hop Resolution Protocol) Resolution Request packet from the received MPOA Resolution Request packet, and transmits it to the MPS 703 of the next hop toward the target 704, referring to the IP routing table (not shown). An MPS like the MPS 702 is called as an ingress MPS.
As described above, the NHRP Resolution Request packet is forwarded from one hop to another toward the target, referring to the IP routing table (not shown).
The MPS 703 transmits an MPOA Cache Imposition Request packet to the MPC of the target 704. It is to notify the target 704 of MAC header information to be added to IP packets, which will be transmitted from the MPC 701 to the target 704 on a shortcut VC.
In the above MAC header information, the MAC address of the target 704 is included as DA (Destination MAC Address), and the MAC address of the node of the MPS 703 as SA (Source MAC Address).
The MPC of the target 704 returns an MPOA Cache Imposition Reply packet to the MPS 703. In the above MPOA Cache Imposition Reply packet, an ATM address for accepting the establishment of a shortcut VC by the target 704 is included.
The MPS 703 which has received the MPOA Cache Imposition Reply packet makes an NHRP Resolution Reply packet, and transmits it toward the MPS 702. The ATM address of the MPC of the target 704 is also included in the above NHRP Resolution Reply packet.
As described above, the NHRP Resolution Reply packet is forwarded from one hop to another toward the ingress MPS 702, referring to the IP routing table (not shown).
The MPS 702 receives the NHRP Resolution Reply packet, and then transmits an MPOA Resolution Reply packet to the MPC 701. The ATM address of the MPC of the target 704 is included in the above MPOA Resolution Reply packet. Thereby, the MPC 701 can obtain information on the ATM address of the target 704.
The MPC 701 establishes a shortcut VC using the ATM address of the target 704, and passes the subsequent IP packets toward the target 704 onto the shortcut VC.
The MPC of the target 704 receives the IP packets from the shortcut VC, and adds the MAC header previously notified by the MPOA Cache Imposition Request packet to the above IP packets. The MAC frames made as described above are seemed as if the node of the MPS 703 transmitted the above MAC frames to the target 704. Thereby, the upper-layer protocol processing of the target 704 may be performed in a similar manner to a case without introduction of the MPOA.
Now, the operations for a case where the target is not in the ATM network will be described, referring to FIG. 15.
It is assumed that a node of an MPC 801 starts to transmit IP packets toward a target 805. The IP packets are forwarded hop by hop through a node of an MPC 801, that of an MPS 802, and that of an MPS 803, toward the target 805.
During the above time, the MPC 801 counts the IP packets. When the above counted value becomes equal to or larger than a predetermined value in a fixed time, (for example, equal to or larger than ten packets in one second), it is judged as “There is a flow”.
The MPC 801 which detects the above flow transmits an MPOA Resolution Request packet which includes the IP address of the target 805 to the MPS 802.
The MPS 802 makes an NHRP Resolution Request packet from the received MPOA Resolution Request packet, and transmits it to the MPS 803 of the next hop toward the target 805, referring to the IP routing table (not shown).
The MPS 803 detects that the target 805 is not on the ATM network. In the above case, an MPOA Cache Imposition Request packet is transmitted to an MPC 804 which is the MPC of the own node, as the node of the MPS 803 is required to be an egress router.
Though the MAC address of the node of the MPS 803 is included as DA in the MAC header information contained in the MPOA Cache Imposition Request packet, for example, the MAC address of the node of the MPS 803 is included also as SA. Some implementation may set SA to “0”.
The MPC 804 returns an MPOA Cache Imposition Reply packet to the MPS 803. In the above MPOA Cache Imposition Reply packet, an ATM address for accepting the establishment of a shortcut VC by the MPC 804 is included.
The MPS 803 which has received the MPOA Cache Imposition Reply packet makes an NHRP Resolution Reply packet, and transmits it toward the MPS 802. The ATM address of the MPC 804 is also included in the above NHRP Resolution Reply packet.
The MPS 802 receives the NHRP Resolution Reply packet, and then transmits an MPOA Resolution Reply packet to the MPC 801. The ATM address of the MPC 804 is included in the above MPOA Resolution Reply packet. Thereby, the MPC 801 can obtain information on the ATM address of the MPC 804 on the egress router.
The MPC 801 establishes a shortcut VC using the ATM address of the MPC 804 on the egress router, and passes the subsequent IP packets toward the target 805 onto the shortcut VC.
The MPC 804 receives the IP packets from the shortcut VC, and adds the MAC header previously notified by the MPOA Cache Imposition Request packet to the above IP packets. Since the DA of the MAC frames made as described above is the MAC address of the node of the MPS 803, upper-layer protocol processing of the node of the MPS 803 may be performed in an approximately similar manner to a case without introduction of the MPOA.
However, the SA of the above MAC frames is not that of the node of the MPS 802, in a different manner from that of the case of FIG. 14. Therefore, the MAC frames are not seemed as if the node of the MPS 802 transmitted the above MAC frames to the node of the MPS 803.
In other words, the above conventional MPOA system has had the following problems.
A major problem is as follows: when a certain MPS node becomes an egress router, for example, as the target is not on the ATM network, the SA of the MAC header information contained in an MPOA Cache Imposition Request packet transmitted from the above MPS to the MPC of the own node is not the MAC address of the MPS node at the previous hop, in a different manner from a case where the target is on the ATM network.
The reason is that the MPS of the egress router has no means for obtaining information on the MAC address of the MPS node at the previous hop.